THEORETICAL AND EXPERIMETAL STUDY ON THE STABILITY OF SOME 4-(4-CHLOROPHENYL)PYRIMIDINIUM YLIDES

Abstract

The stability of ylides derived from 4-(4-chlorophenyl)pyrimidinium was studied theoretically and experimental. The study was based on semiempirical methods of quantum mechanics, this is PM3 method of HYPERCHEM software, as well as those of molecular mechanics using MM2 method. In order to establish a correlation between structure, stability, and reactivity in 4-(4-chlorophenyl)pyrimidinium ylides series, we have achieved a theoretical study based on use of relativist disturbance theory of the second order limited to border molecular orbitals. As in the case of 4-(4-chlorophenyl)pyrimidine was aimed energetic minimization of the molecule by PM3 semiempirical method, each structure was optimized until the energy change was smaller than 0,001 kcal/mol. Increment of rotation was about 15°. Atomic charge,  pz atomic orbitals coefficients, as well as values of energy of border molecular orbitals HOMO and LUMO  of atoms from analyzed 4-(4-chlorophenyl)pirimidinium ylides were calculated using PM3 semiempirical  method. The fact that total atomic charges are sub-unitar indicates an advanced delocalization of negative charge from ylidic carbanione on its substituents and of positive charge from nitrogen N-ylidic atom on the entire heterocycle. The structure of compounds was proved by elemental and spectral (IR, RMN și SM)  analysis. Elemental analysis (C, H, N) and spectral data are in accordance with the proposed structure